JP-2004-190586A describes a combustion system in which fuel is reformed by a catalyst of a reformer and the reformed fuel is injected into an intake pipe to be combusted in a combustion chamber. A combustion energy is increased and a fuel economy can be improved.
In the above combustion system, an ignition-type engine is used. When the combustion becomes unstable at a starting of the engine, a port injection is conducted to ignite the fuel. At the times other than the starting of the engine, the fuel is reformed to improve self-ignitionability thereof. The reformed fuel time is directly injected into a combustion chamber to be self-ignited. Non-reformed fuel which has not been reformed is also injected into the combustion chamber through an intake port. The reformed fuel and the non-reformed fuel are combusted at the same time. The reformed fuel flows through an intake pipe and is mixed with a fresh intake air to be cooled. In a case that ambient temperature is low and temperature of the reformed fuel supplied to a reformer is low, an ignitionability may be deteriorated.
In the above conventional combustion system, the fuel is reformed in order to improve the self-ignitionability. Meanwhile, the present inventor studied about the reformed fuel in order to increase the combustion energy of the fuel per unit quantity so that the fuel economy is improved.
For example, alcohol fuel (CH3—OH), such as methanol and ethanol, is reacted to water (H2) on a catalyst, whereby the fuel is changed into hydrogen (H2) and carbon monoxide (CO). Such hydrogen and carbon monoxide are combusted as the reformed fuel.
However, according to the inventor's study, when the above fuel reform is conducted to improve the combustion energy, the self-ignitionability is deteriorated. It is becomes difficult to perform a compression self-ignition combustion of the reformed fuel.